The present invention relates to an apparatus for producing threaded closures. Such closures include metal closures which are commonly used on a variety of bottles and jars such as mayonnaise jars, cosmetic containers, medicine bottles, and the like. The metal closures threaded in accordance with the invention includes metal shells having cylindrical walls. The screw threads are formed inwardly on the cylindrical wall.
Various methods are known for threading closures. For example, see U.S. Pat. Nos. 2,209,416 and 2,465,253. In the former, one method is disclosed which uses two expanding thread forming tools in series. The first tool forms a first thread segment leaving intervening unthreaded areas, and the second tool forms second thread segments in the unthreaded areas, thus completing the thread.
The latter patent achieves the formation of the closure thread by insertion, into the closure, of a tool having a diameter smaller than the closure diameter. This results in the tool having to make more than one revolution as it moves around the closure sidewall. Due to this requirement of a one-plus revolution, it has been found that thread accuracy is compromised--especially affected is thread pitch.
As can be appreciated, these two methods have drawbacks. The first method requires two threading steps and apparatuses. The second method is not capable of providing the accuracy which is characteristic of high quality closures.
Thus, it is an object of this invention to provide an apparatus which, in a single step, can form the closure thread while the closure is held in the apparatus used to carry the closure to and from prior closure forming stations.